Study Provides Key Insights on LED T8 Replacements for Strip, Wrap and Pendant Fixtures

LED T8 replacement lamps for existing fluorescent T8 linear tubes have emerged as a priority consideration for facility managers in office, school, warehouse, hospital/medical, restaurant, grocery and other applications. The promise of significant energy savings and lower maintenance costs, plus the relative simplicity of most LED replacement projects, has motivated this interest.

In addition, on a macro level, the extremely large installed base of linear fluorescent lamps in the U.S. – 2.5 billion lamps by some estimates – few if any LED options offer the potential impact on the national electric energy system.

While the opportunities seem obvious, the number of LED T8 product configurations and installation variations has introduced enough complexity in the market to slow implementation.

Manufacturers currently offer LED T8 lamps in these operation types:

Type A: LED lamp is driven by the existing fluorescent instant or programmed start ballast.

Type B: LED lamp is driven by line voltage that bypasses the existing fluorescent ballast.

Type C: LED lamp is driven by a separate LED driver.

Type A/B: Hybrid that allows lamp operation use either Type A or Type B approach.

Type A/C: Hybrid that allows lamp operation use either Type A or Type C approach.

To help sort through the pros and cons of these types of LED T8 lamp replacements, this post will review and summarize a field study and evaluation of LED T8 lamps done in 2017 by Pacific Gas & Electric (PG&E) in conjunction with the University of California at Davis.

Background and Testing Parameters

Using data from various sources, the researchers found that over 85% of the linear fluorescent fixtures in the U.S. used 4 foot lamps in 2 lamp and 3 lamp configurations. For the California study, these configurations were used for testing LED replacement performance in three types of fluorescent fixtures: strip, wraparound (wrap) and pendant. Troffers were omitted because of the research already done for that fixture type.

The study focused on comparing light output, efficacy and light distribution.

Lamp Specs

Fluorescent Lamps

  • T8: 4 foot, 32 watt
  • T8: 700 Series (in California, the majority of existing fluorescent linear lamps have a color rendering index, CRI < 80)
  • Ballast: electronic, normal ballast factor
  • Primary fixture configuration: 2-lamp

LED Lamps

  • LED lamps were selected based on manufacturer product information designating the lamps as replacements for 4 foot, 32 watt T8 linear fluorescent.
  • All LED lamps had a color temperature specification of 4000K.
  • All LED tubes were frosted.
  • When available, dimmable LED T8’s were used.

These parameters were applied for the LED lamps that were used in the study. Lamps were selected to include all the operation types described above – Type A, B, C, AB, AC.

Test Results

Type A (uses existing ballast):

  • System Efficacy (included ballast): The LED system provided a substantial improvement in efficacy -100 to 118 lm/W for LED compared to 59 to 82 lm/W for fluorescent (the pendant direct/indirect fixture was an exception, see discussion below).
  • Light Output: The LED system delivered significantly less light (14% to 30%) than the fluorescent lamps in nearly all cases. Wrap fixtures with LED lamps performed best with only a 6% lower light output, which would not be noticed by most occupants. The reason: heat accumulation inside the wrap fixture caused the fluorescent lamps to have lower light output. The heat did not have a similar impact on the light output of the LED lamps, explaining the minimal difference in output between the two sources. Note: the heat might have an impact on LED lamp life, but that factor was not part of this study.
  • Easiest installation, but lowest overall performance because energy is consumed by the ballast in addition to the lamp.

Type B (uses line voltage, bypasses existing ballast)

  • System Efficacy: The LED system provided a substantial improvement in efficacy – 72 to 138 lm/W for LED compared to 59 to 82 lm/W for fluorescent (pendant direct/indirect fixture was an exception, see below).
  • Light Output: The LED system delivered significantly less light (13% to 35%) than the fluorescent lamps in nearly all cases. Wrap fixtures again performed best for the same reason described above for Type A.
  • Mid-range overall performance compared to other options.
  • Important consideration: Type B products are UL certified as a component only which may void the UL certification of the fixture.

Type C (uses separate LED driver, bypassed existing ballast)

  • System Efficacy: The LED system provided a substantial improved in efficacy – 88 to 135 lm/W for LED compared to 59 to 82 lm/W for fluorescent.
  • Light Output: The LED system delivered the same or higher light output than fluorescent.
  • Highest overall performance compared to Types A or B
  • To achieve this strong performance, the LED driver used in the system must match the one specified by the lamp manufacturer.

Additional Observations

Wrap fixtures are designed with no uplight component. Surface mounted on ceilings and walls, these fixtures provide general ambient illumination. As noted above, in wrap fixtures, the LED lamps delivered close to the same light output as fluorescent lamps at much higher efficacy. The diffuser encloses the lamp cavity completely. The researchers concluded that the heat accumulation inside the wrap fixture affected the light output of fluorescent lamps more than LED. This factor makes LED T8 replacements a good choice for wrap fixtures.

Pendant fixtures utilizing both direct and indirect distribution are not a good fit for LED lamp replacement.

The heat sink on LED bulbs runs the length of the bulb which restricts the beam angle to less than 360°.

 

This photo shows a cut-away of an LED T8 lamp. The red line outlines the heat sink that runs from one end of the lamp to the other. Obviously, no light distribution can occur in the upward direction.

For pendant fixtures that have both up and downlight distribution, the restricted beam of LED prevents them from providing the uplight component of the light distribution.

 

Summary

For Type A and B LED lamps, the researchers concluded “. . . linear LEDs marketed to replace standard 4 ft linear fluorescents cannot compete in terms of total light output . . . the overall energy savings are achieved, in part, by reducing light output, not just power.” The one exception was wrap type fixtures that virtually matched the light output of fluorescent.

Finally, the study clearly showed that LED T8 lamps using the Type C configuration provide the best overall performance. LED T8 lamps operated by an LED driver specifically designed for the lamp will produce equivalent light output to fluorescent with significant higher efficacy and much longer lamp life.

Download the complete study for additional information.

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Dave Burtner

Dave has been active in the lighting industry since 1994. Formerly a member of the Illuminating Engineering Society of North America and certified by the National Council On Qualifications for Lighting Professionals, Dave now writes blog posts, lighting tips and provides lighting product assistance for the Topbulb website.

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